Have a cough that seems to be worse at night?

A postnasal drip can irritate the throat and cause a cough that becomes worse at night as more dripping occurs when you are lying down to sleep. — Wikimedia Commons

Postnasal drip is a condition when more mucus than average gathers from your nose or sinuses, and drips down the back of your throat or pharynx.

You will naturally have mucus because the glands in your nose and throat make it.